1. Field of the Invention
The invention is directed to a voltage regulator whose input is connected to a first supply voltage and whose output voltage at an output is supplied in normal operation via a feedback line to an input of an integrated circuit having a circuit block for driving the actuator in order to assure the monitoring and regulating of the output voltage to a predetermined first voltage value.
2. Description of the Related Art
For both clocked as well as linear voltage regulators, it is necessary that the regulated output voltage is constantly monitored by a regulator in order to immediately provide correction when a deviation from a rated value is detected. This allows the output voltage to be kept constant. Linear voltage regulators are known, for example, from Tietze, Schenk, Halbleiterschaltungstechnik, 10th Edition, Springer-Verlag, 1993, pages 542 through 555. Clocked voltage regulators, for example, in the form of an up or of a down converter, are described on pages 563 through 571 in the same reference.
For a clocked voltage regulator, when the output voltage drops below a predetermined value, the duty cycle of the switch is increased by a drive so that the output voltage again approaches the predetermined rated value. Generating a constant output voltage at a predetermined rated value is thus based on a constantly operating control circuit. One problem arises for this device when the line with which the voltage regulator monitors the output voltage is interrupted. As a rule, the input node of the drive circuit is internally connected to ground through some resistance so that the voltage at the input node drops to zero in the case of a line interruption. The voltage regulator must then assume that its output voltage is too low and thus attempts to increase the output voltage above the rated value without taking potentially connected users into consideration. This leads to damage to the connected users if additional, external protective measures at the users end are not provided.